1. Field of the Invention
The present invention relates to a micro electromechanical system (MEMS) relay, and more particularly, to a MEMS relay in which two switches that are integrated in one structure are turned on/off opposite to each other in seesaw fashion.
2. Description of the Related Art
As techniques for manufacturing semiconductor integrated circuits have been developed, the size of active devices used in electronic products has been considerably reduced. However, the size of passive devices, such as a relay, a variable capacitor, and a variable inductor, has not been sufficiently reduced. Thus, the reduction of the size of passive devices has become an important problem awaiting solution.
Most conventional MEMS relay switches comprise a single switch. In the case of a plurality of switches, each of the switches operates independently of the others, as disclosed in U.S. Pat. No. 5,619,061. FIG. 1 is a schematic plan view illustrating a conventional MEMS relay disclosed in the above U.S. patent. Referring to FIG. 1, if pull-down voltage is applied to a control electrode 1 of switches each having an input signal electrode IN and an output signal electrode OUT1 or OUT2, a metal plate 2 is bent down due to an electrostatic force acting between the control electrode 1 and the metal plate 2 such that the metal plate 2 partially contacts the input and output signal electrodes IN and OUT1 or OUT2. Two switches shown in FIG. 1 can operate independently by the control electrode 1.
However, the conventional MEMS relay has the following problems. When the metal plate 2 is isolated from the input and output signal electrodes IN, and OUT1 and OUT2, in other words, when the MEMS relay is turned off, the metal plate 2 may swing. In addition, it is necessary to increase the area of the MEMS relay in order to perform wire-bonding on the MEMS relay during packaging, and accordingly, the packaging area where the MEMS relay switch is packaged is also increased.
To solve the above-described problems, it is a first object of the present invention to provide a MEMS relay that is structurally stable and is compact, in which two switches are integrated into one structure but operate opposite to each other.
It is a second object of the present invention to provide a method of fabricating the MEMS relay.
Accordingly, to achieve the first object, there is provided a MEMS relay which comprises a first wafer, a second wafer, and a third wafer that are sequentially stacked. The first wafer includes driving electrodes positioned at the bottom surface of the first wafer, input signal electrodes and output signal electrodes formed adjacent to each other and corresponding to the driving electrode, via holes formed through the first wafer on the driving electrodes, the input signal electrodes, and the output signal electrodes, and metal pads formed over the via holes. The second wafer includes a body including a sealing unit used to hermetically seal the first and third wafers with the second wafer interposed therebetween, a driving unit which is formed inside and isolated from the body, is an integrated body consisting of a silicon substrate, a passivation layer formed on the silicon substrate, and contact electrodes formed on the passivation layer, and is located lower than the top surface of the body by a predetermined distance, and a connection supporter which extends from two opposing sides of the driving unit to the corresponding inner surface of the body. The third wafer includes a hollow in which the driving unit can be rotated.
Preferably, the connection supporter includes a torsion spring, which extends from the two opposing sides of the driving unit outwardly, and an anchor which connects the torsion spring to the corresponding inner surface of the body.
Preferably, an electrode supporter is further formed on the third wafer to support each of the input and output signal electrodes.
Preferably, the second wafer is formed of silicon, and the first and third wafers are formed of Pyrex glass.
Preferably, the passivation layer is a SiO2 layer or a Si3N4 layer.
Preferably, ball grid arrays (BGAS) are further formed on the metal pads.
To achieve the second object, there is provided a method of fabricating a MEMS relay including (a) preparing a silicon wafer as a second wafer and two Pyrex glass wafers as first and third wafers, (b) forming a mask on the second wafer and anisotropically etching the second wafer using the mask, (c) forming a passivation layer in the middle of the second wafer and forming contact electrodes on the passivation layer by patterning, (d) forming electrodes at the bottom of the first wafer by patterning, (e) bonding the first and second wafers to each other, (f) planarizing the upper portion of the first wafer by chemical mechanical polishing (CMP), forming via holes through the first wafer, and forming metal pads over the via holes, (g) planarizing the lower portion of the second wafer by CMP, and patterning and etching the bottom portion of the second wafer, (h) forming a hollow in the third wafer by etching a predetermined portion of the third wafer, and (i) bonding the third wafer to the lower portion of the second wafer.
Preferably, the method further includes forming BGAs on the metal pads after the step (f). Preferably, in the step (i), the third wafer and the second wafer are anodically bonded to each other.